Water spots are the minerals left behind when water evaporates off your vehicle surface, what those minerals are differs depending on what was in the water, which is different depending on where you are and your water source, if it's from the tap, or rain, sprinklers or tank water.  Most of these in New Zeeland are alkaline like lime and can be removed by using a water spot remover that is a light acid.  It dissolves the minerals, you then wipe it off and neutralize it with water or quick detailer.  Sometimes a wash with an Acidic wash like Fireballs pH3 will be enough.

Water spot removers are a great tool but they are just that a tool.  They will dissolve most minerals, but not all.  And if you have had water spots on a while they can etch into the surface physically removing the top layer of the surface eroding it, this means even when removed you may see marks still there from this erosion.  Water spot removers are verry effective but have their limitations.  If water spot remover will not remove the marks then you may need to step up to machine polishing.  

We recommend applying layers or protection onto your paint to help prevent watersports and make them easier to remove. 

The Chemical Guys water spot remover is stronger than the fireball and Zephyr water spot removers which are stronger than the pH3 acidic wash.